When graphic novelist Alan Moore (Watchmen, League of Extraordinary Gentlemen) was asked by a fan what “happens” to him when he writes, this is in part how he replied:

I know that my consciousness, if I am immersed in writing something demanding, is moved into a completely different state than the one which I inhabit during most of my waking life…

When you descend into this level of our reality, the code of our reality if you like, then whether consciously or not; whether deliberately or not, you are working magic. So, the answer to your question as to what happens to me when I write, is the most banal and useless answer you will ever get from an author: the magic happens…

One of the secrets to writing, it would seem, is to allow yourself to descend into that fugue state and just let the magic work its way through you.

It seems to have worked for Moore.